FIG. 8 is a partial sectional view of a conventional magnetic sensing element (spin-valve thin-film element), taken in a direction parallel to the surface facing a recording medium.
As shown in FIG. 8, a seed layer 2 composed of NiFeCr, or the like, is disposed on an underlayer 1 composed of Ta. A multilayer film T is disposed on the seed layer 2, the multilayer film T including an antiferromagnetic layer 3, a pinned magnetic layer 4, a nonmagnetic layer 5, a free magnetic layer 6, and a protective layer 7 deposited in that order from the bottom.
The free magnetic layer 6 and the pinned magnetic layer 4 are each composed of a Heusler alloy such as Co2MnGe, the nonmagnetic layer 5 is composed of Cu, the antiferromagnetic layer 3 is composed of PtMn, and the protective layer 7 is composed of Ta.
An exchange coupling magnetic field is produced at the interface between the antiferromagnetic layer 3 and the pinned magnetic layer 4, and the magnetization of the pinned magnetic layer 4 is pinned in the height direction (in the Y direction).
Hard bias layers 8 composed of a hard magnetic material such as CoPt are disposed at both sides of the free magnetic layer 6. The top, bottom, and ends of each hard bias layer 8 are isolated by an insulating layer 9. The magnetization of the free magnetic layer 6 is aligned in the track width direction (in the X direction) by a longitudinal bias magnetic field from the hard bias layers 8. Electrode layers 10 are disposed on the top and bottom of the multilayer film T.
When an external magnetic field is applied to the magnetic sensing element shown in FIG. 8, the magnetization direction of the free magnetic layer 6 is changed relative to the magnetization direction of the pinned magnetic layer 4, resulting in a change in the resistance of the multilayer film T. When a sensing current with a constant current value flows, the change in the resistance is detected as a change in voltage, and thus the external magnetic field is detected.
A magnetic sensing element including a pinned magnetic layer composed of a Heusler alloy is described in Japanese Unexamined Patent Application Publication No. 2003-309305 (page 8 and FIG. 4).
The free magnetic layer 6 and the pinned magnetic layer 4 composed of a Heusler alloy, such as a Co2MnGe alloy or a Co2MnSi alloy, have a body-centered cubic lattice crystal structure in which the {110} planes are preferentially oriented in a direction parallel to the surfaces of the layer. The nonmagnetic layer 5 composed of Cu has a face-centered cubic lattice crystal structure in which the {111} planes are preferentially oriented in a direction parallel to the surfaces of the layer.
In the conventional magnetic sensing element, the free magnetic layer 6 and the pinned magnetic layer 4 have the crystal structure that is different from the crystal structure of the nonmagnetic layer 5. Moreover, there is a large difference in lattice constant between them. Therefore, the degree of lattice matching between the free magnetic layer 6 and the nonmagnetic layer 5 and the degree of lattice matching between the pinned magnetic layer 4 and the nonmagnetic layer 5 is low. Consequently, lattice defects occur in the free magnetic layer 6 and the pinned magnetic layer 5. For example, irregular phases in which the L21-type crystal structure is not allowed are generated. As a result, the spin-dependent bulk scattering coefficient β of the free magnetic layer 6 or the pinned magnetic layer 5 is decreased. Furthermore, diffusion at the interface between the Heusler alloy and the nonmagnetic layer 5 easily occurs, and as a result, the spin-dependent interface scattering coefficient γ at the interface between the free magnetic layer 6 and the nonmagnetic layer 5 or at the interface between the pinned magnetic layer 4 and the nonmagnetic layer 5 is decreased.
The decrease in the spin-dependent bulk scattering coefficient β of the free magnetic layer 6 or the pinned magnetic layer 5 and the decrease in the spin-dependent interface scattering coefficient γ at the interface between the free magnetic layer 6 and the nonmagnetic layer 5 or between the pinned magnetic layer 4 and the nonmagnetic layer cause a decrease in the read output of the magnetic sensing element.